Abstract
Aim The two species of ground parrots ( Pezoporus wallicus and P. flaviventris ) are morphologically and behaviourally similar, yet geographically disjunct and genetically distinct. We investigated the dynamics of divergence between the two species in the context of niche evolution across Australian platycercine parrots. Location Australia. Taxon Platyercine parrots. Methods We estimated climatic and habitat niche breadths for all Australian platycercine parrots and quantified niche overlap between species. We constructed climate envelope niche models for ground parrots to project paleoclimatic suitability, and reconstructed biogeographic and climatic niche evolution of platycercine parrots using phylogenetic comparative methods. Results We found that the western ground parrot ( P. flaviventris ) occupies a narrow climatic niche almost entirely nested within the broader niche of the eastern ground parrot ( P. wallicus ), which has the widest climatic niche of any Australian platycercine. Habitat niches also differ markedly, with P. flaviventris specialised to mallee and heathland vegetation, and P. wallicus using a wider array of habitats. Palaeoclimate projections suggest a formerly contiguous range across southern Australia that became fragmented ~2 Mya, coinciding with increasing aridity across the Nullarbor plain. Evolutionary models support niche expansion in P. wallicus , consistent with speciation following allopatric isolation and subsequent ecological divergence. Main Conclusion Our findings provide evidence for ecological speciation under niche conservatism and have important implications for conservation management of the Critically Endangered P. flaviventris , including consideration of genetic rescue strategies involving P. wallicus .